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A three-decade-old international treaty to phase out chemicals that deplete the ozone layer that protects our planet from harmful solar radiation is paying off.
Thanks to the Montreal Protocol of 1987, the ozone layer continues to regenerate, according to the scientific assessment of the depletion of the 2018 ozone layer released Monday by the I & # 39; World Meteorological Organization and the United Nations Environment Program.
This includes the "hole" over Antarctica where the ozone layer is exceptionally fine, which is shrinking gradually since the early 2000s and is expected to subside by the 2060s. This year, the hole covered about 9 million square miles, a slightly smaller area than the entire North American continent.
"Generally, it's good news," said Paul Newman, co-chair of the new Evaluation Committee and Chief Science Officer of Earth Sciences at NASA's Goddard Space Flight Center. Ozone-depleting gases are declining and have continued to decline since the mid-1990s. "Projections for the future are quite positive as long as the parties continue to comply with the Montreal Protocol."
Ozone, a molecule composed of three atoms of oxygen, occupies two regions of the atmosphere. Ten percent of atmospheric ozone is in the troposphere, which extends from ground level to an altitude of about seven miles. At ground level, ozone is an atmospheric pollutant of smog formed from by-products of vehicle exhaust gases and the burning of fossil fuels.
Then there is the ozone layer, a 50 km wide buffer zone that naturally occurs above the troposphere and protects the Earth from the sun's ultraviolet B rays. A cyclic reaction occurs in this band: solar radiation divides the elemental oxygen (O2) into individual oxygen atoms that react with other elemental oxygen molecules to form ozone (O).3), which is reconverted to elemental oxygen when it absorbs radiation. Without this reaction, life on earth could not exist. More harmful radiation would reach the Earth, increasing the risk of skin cancer, cataracts and suppression of the immune system in humans, as well as damage to plants and most aquatic organisms.
In the mid-1970s, scientists discovered that artificial gases containing chlorine and bromine atoms, such as chemicals released by refrigerators, air conditioners and aerosols, could escape into the upper atmosphere. There, they are transformed by ultraviolet rays into chlorine and bromine radicals that initiate the chain reactions that destroy ozone.
Then, in 1985, scientists discovered a hole in the developing ozone layer over Antarctica. Knowing that chlorine-containing compounds, including chlorofluorocarbons, could deplete the ozone layer, 46 countries have been pushing for the regulation of ozone-depleting gases under the Montreal Protocol. by all the countries of the world.
Controlled substances under the Protocol include chlorofluorocarbons, hydrochlorofluorocarbons, carbon tetrachloride, methyl chloroform, and bromine-containing halons and bromide. Assuming that the Montreal Protocol is still applied, ozone in the northern hemisphere is expected to return to healthy levels in the 2030s, ozone in the southern hemisphere in the 2050s, and ozone in the southern hemisphere. the polar regions – where depletion is most severe – in the 2060s. The reduction of ozone-depleting substances, which are also powerful greenhouse gases, has helped to reduce the impact of ozone depletion. avoid at least several centimeters of future sea level rise in the world, according to the assessment.
That's not to say that there are no flies in the ointment, says Newman.
Some ozone – depleting substances, such as chlorofluorocarbon 11 (CFC – 11), decrease less rapidly in the atmosphere than expected. Two independent networks have confirmed an increase in emissions in East Asia since 2012, although their exact origins are still under study.
This is disturbing because compounds, including CFC-11, are banned by the Montreal Protocol and persist in the atmosphere for decades. If anyone releases them today, he will continue to do damage for generations to come.
To make this point, Newman keeps a small box of CFCs in his office – chlorofluorocarbon 12, the original Freon refrigerant. Although CFC-12 represents a significant improvement over the toxic and sometimes deadly refrigerants used before the 1930s, it was not perfect. "If I had to dump this tin on my floor," says Newman, "five percent of that amount would still float in the atmosphere in 300 years".
To make matters worse, once a CFC molecule reaches the high stratosphere, it is broken by ultraviolet rays to release chlorine atoms. A single atom of chlorine can destroy thousands of ozone molecules during its lifetime before being sent back to the lower atmosphere and completely evacuated.
That is why it is important for the parties to comply with the Montreal Protocol and the Kigali Amendment added in 2016. Newman says both treaties have or will have a real effect on reducing emissions.
The Kigali amendment, which will enter into force in January 2019, concerns chemicals used to replace those banned by the Montreal Protocol. The replacement hydrofluorocarbons (HFCs), commonly used in air conditioning units of cars, do not live as long as CFCs and do not destroy ozone, but possess greenhouse gas properties until they reach the end of their life cycle. several thousand times more powerful than carbon dioxide.
With Kigali's amendment in place, we could avoid an increase in global surface temperature of between 0.2 and 0.4 degrees Celsius, depending on the assessment.
As the planet has already warmed to a degree Celsius over the last century and as global temperatures are about to increase by at least a degree by the end of this century of the century, the report states that the elimination of these substances would have "substantial" benefits.
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